The present invention relates to multi-head embroidery sewing machines equipped with a plurality of machine heads each having a plurality of sewing mechanical components that include a needle bar, thread take-up lever and presser foot.
The multi-head embroidery sewing machines are equipped with a plurality of machine heads each including a needle bar, thread take-up lever, presser foot, etc., and rotary hooks corresponding to the heads. In typical examples of the conventionally-known multi-head embroidery sewing machines, the needle bar, presser foot, thread take-up lever, etc. are driven in an interlocked manner by a single drive shaft (main shaft), extending through all of the machine heads, via power converting elements (cams, gears, etc.) provided in the individual machine heads. However, in these typical examples, motion conversion between the needle bar, thread take-up lever and presser foot was impossible. Japanese Patent Application Laid-open Publication No. HEI-4-51991 (hereinafter referred to as Patent Literature 1) and U.S. Pat. No. 5,474,001 (which corresponds to the No. HEI-4-51991 publication and will hereinafter be referred to as Patent Literature 2) disclose a technique which permits motion conversion between the needle bar, thread take-up lever and presser foot by driving these components by separate or individual drive sources.
In the multi-head embroidery sewing machine disclosed in Patent Literature 1, individual drive sources (e.g., motors) for driving the needle bars, thread take-up levers and presser feet, respectively, of all of the machine heads; namely, the drive sources for driving the needle bars, thread take-up levers and presser feet are shared among the machine heads, and drive shafts, driven by the respective drive sources (motors), extend through all of the machine heads for shared use among the machine heads. In each of the machine heads, rotation of the drive sources is transmitted to corresponding mechanisms of the needle bar, thread take-up lever and presser foot. Thus, although motion conversion is permitted between the mechanisms of the needle bar, the thread take-up lever and presser foot through separate control of the individual motors, the respective motions of the thread take-up lever and presser foot are all the same among the machine heads. Therefore, whereas the disclosed sewing machine is suited to sew embroidery products with stitch formation (conditions) common to the individual machine heads, it is not at all suited to sew embroidery products with stitch formation differing among the machine heads. However, because the essential technical idea of the multi-head embroidery sewing machines is, as well known, to sew same embroidery patterns with same stitch formation via a plurality of parallel machine heads to thereby mass-produce embroidery products, no particular inconvenience has heretofore been felt from the viewpoint of the conventional technical idea.
Further, Japanese Patent Application Laid-open Publication No. HEI-4-347192 (hereinafter referred to as Patent Literature 3) discloses a multi-head embroidery sewing machine, in which independent or separate drive sources (motors) for individually driving a needle bar, thread take-up lever and presser foot are provided per machine head and in which a separate drive source (motor) for driving a rotary hook is also provided per machine head.
However, the sewing machine disclosed in Patent Literature 3 too is merely based on the aforementioned conventional technical idea; namely, Patent Literature 3 discloses nothing more than providing independent drive sources (motors) per machine head. Further, form of control disclosed in Patent Literature 3 is not so different from that disclosed in Patent Literature 1, and the control is only intended to permit motion conversion between the mechanisms of the needle bar, thread take-up lever and presser foot through separate control of the motors for the needle bar, thread take-up lever and presser foot. In addition, with the sewing machine disclosed in Patent Literature 3, effectiveness of the provision of the rotary hook drive source (motor) per machine head was not considered sufficiently. Namely, it was not considered that the rotary hook drive source (motor) provided per machine head would rather become superfluous equipment for the rotary hook that is subjected to only a small load.
The aforementioned technical ideas of the conventional multi-head embroidery sewing machines is based on the concept that same embroidery products only have to be completed on all of the machine heads with embroidering workpieces (such as fabric or leather) having same characteristics (thickness, degree of stretchability, etc.) set on the individual machine heads and with upper threads having same characteristics (thickness, degree of stretchability, etc.) used for sewing. However, in the embroidery product manufacturing industry too, there has recently been an increasing demand for small-lot production of a wide variety of products. Nevertheless, the conventionally-known multi-head embroidery sewing machines of the type which mass-produce same products can not at all satisfy such a demand for small-lot production of a wide variety of products.
Further, in the multi-head embroidery sewing machine disclosed in Patent Literature 1, where the drive shafts extend through all of the machine heads, as the number of the machine heads increases, the drive shafts have to have increased lengths, so that the rotationally-driven drive shafts tend to undesirably twist. For example, a relative great twist or torsion tends to be produced in the drive shaft for a needle bar driving mechanism, which would result in relatively great time differences in up-and-down movement between the machine heads located remotely from each other. Such great operation time differences would lead to time differences in needle and rotary hook motion between the machine heads located remotely from each other and hence to deviations in stitch formation between the machine heads. Further, phase differences in thread take-up lever motion between the machine heads could cause desynchronization between the motion of the thread take-up levers and the rotation of the rotary hooks, which would also lead to differences in stitch formation between the machine heads. Thus, even where embroidering workpieces and threads of same material and characteristics are used in all of the machine heads, it would be difficult to obtain embroideries of the same quality. The greater the number of the machine heads, the more pronounced such unwanted tendencies become. Thus, although the greater number of the machine heads can advantageously achieve a greater number of embroidery products, it would simultaneously present the demerit that embroidery products of the same quality can not be obtained in all of the machine heads. Further, because all of the machine heads are driven by the common elongated drive shafts, the drive shafts themselves tend to produce great vibration and sound noise, and this tendency would become more serious as the number of the machine heads increases and as the rotating speed of the drive shafts increase. Therefore, the conventionally-known embroidery sewing machine could not achieve an increased operating speed, although strenuous efforts have been made so far to create effective anti-vibration measures.
Furthermore, when there has occurred a need for repair work involving component part replacement in any of the machine heads in the conventionally-known multi-head embroidery sewing machines, it is necessary for a human operator to perform the repair work consuming great amounts of time and labor. In addition, during the repair work, the embroidery sewing machine has to be placed in a complete non-operating (deactivated) condition, which would cause a lot of inconveniences to a user of the sewing machine. For example, when repair work requiring replacement of a cam for driving the needle bar or thread take-up lever in the sewing machine of the type disclosed in Patent Literature 1, the drive shaft extending through all of the machine heads has to be taken out or removed; for such a purpose, the human operator has to perform extremely troublesome repair operation, e.g. first loosening all couplings of cams etc. in all of the machine heads, then taking out the drive shaft, removing the deficient component part, setting a replacing component part while again passing the drive shaft through all of the machine heads and then again coupling the cams etc. in all of the machine heads.
Furthermore, in the conventionally-known embroidery sewing machines, machine heads corresponding to different types of sewing, such as ordinary sewing and special sewing (e.g., strand-like or string-shaped material sewing) machine heads, are mounted fixedly. Thus, it has heretofore been inconceivable to replace, for example, an ordinary sewing (lock-stitching) machine head with a “handwheel-operated machine head” (or handwheel-operated lock-stitching machine head capable of sewing a string-shaped material, such as a tape or cord, onto a fabric) or vice versa in the same sewing machine. Further, in the conventionally-known embroidery sewing machines, which are constructed to select same needle bars (i.e., same color threads) concurrently in all of the machine heads, it is not possible to make, in a concurrent, parallel fashion, embroideries having different color-thread patterns although having a same outline design.